In the past year we focused on identification of the number of rotaviral structural and nonstructural proteins. As many as 15 SA-11 proteins were identified and 10 of the 15 were structural. Less success was realized with some of the other animal rotaviruses as well as with one human strain (Wa), for which 10 to 12 proteins were identified. Six or seven of them were structural. Emphasis was placed on developing methods to increase the yield of cell cultures infected with the more fastidious human strains in order to obtain higher titered stocks for use in biochemical studies. Additional efforts were made to develop methods of labeling rotaviral proteins in cell lysates with 35S methionine. These lysates were used to identify specific proteins which were immunoprecipitated by monoclonal antibodies. In order to obtain infected cell lysates which were suitable for immunoprecipitation experiments with monoclonal antibodies we developed a modification of a published method which had been successful for similar studies with reoviral monoclones. The method produced labeling of all of the proteins found previously in infected MA104 cells labeled by one standard method.